Electric motor for driving a piston pump and method of assembly

ABSTRACT

An electric motor for driving a piston pump assembled thereto is disclosed wherein a load from the piston pump acts radially on an armature shaft of the electric motor. The electric motor is assembled such that the outer ring of a yoke bearing is connected to a yoke, and the outer ring of a first pump housing bearing is press fit to a pump housing. One end of the armature shaft is press fit to the yoke bearing inner ring, and the other end of the armature shaft is press fit to the first pump housing bearing inner ring. Thus, wobbling of the armature shaft in the axial and radial directions is minimized or eliminated.

This is a Division Application Ser. No. 08/884,471 filed Jun. 27, 1997.The entire disclosure of the prior application is hereby incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to the art of electric motors. This invention isspecifically concerned with electric motors for driving piston pumpsused in anti-locking brake devices for vehicles and the like.

2. Description of Related Art

Generally, examples of electric motors for driving piston pumps of thistype include arrangements wherein the piston is caused to movereciprocally in the radial direction with respect to the armature shaftof the driving motor, e.g., arrangements used for anti-locking brakes.An example of such an arrangement is disclosed in Japanese Unexaminedpatent Publication No. 2-207184. In this arrangement, bearing of thearmature shaft is accomplished by a pair of bearings provided at eitherside of an eccentric shaft linked to the piston side. The armature shaftis press fit to the inner ring of the pair of bearings. The armatureshaft is press fit to the bearings when the shaft is aligned with eachof the bearings. In the event that the outer rings of the bearings arepress fit to the pump housing side, freedom in the radial direction islost, and in the case that there is misalignment in both of thebearings, press fitting of the armature shaft cannot be performed forall practical purposes. Accordingly, the bearings are arranged so as tobe loosely inserted into the pump housing to ensure freedom in theradial direction, however slight, thus handling misalignment.

However, with such an arrangement, not only does wobbling of thebearings in the radial direction due to receiving the load from thepiston moving in the aforementioned radial direction cause noise anddeterioration of pump performance, but other parts become necessary inorder to prevent the bearings (which have been inserted loosely) frommoving in the axial direction, requiring extra parts and complicatedassembly. Because it is necessary to provide a space for setting a jigfor assembling both bearings in a pump housing separately from a spacefor piston pump components, the resulting space for piston pumpcomponents becomes smaller, which creates a problem in that freedom inlayout for the piston pump components in a pump housing is reduced.

In order to deal with such problems, an arrangement has been disclosedin Japanese Unexamined patent Publication No. 7-184344, wherein groovesare provided in the bearing outer ring and the member of the pumphousing to which the bearing is to be inserted. Resin material isinserted into the aforementioned grooves so as to restrict movement inthe axial and radial direction.

However, with such an arrangement, the endurance of the resin materialis problematic, and not only is there the possibility that the bearingsmay return to the original state of being inserted loosely due todeterioration and the like of the resin over prolonged usage periods,but there is the problem that resin material in the grooves decreaseswork efficiency.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to solve theabove-mentioned problems. The invention includes an electric motor whichdrives a piston pump such that the load from the piston pump side actsupon the armature shaft in a radial direction.

In accordance with a first aspect of the invention, an electric motorfor driving a piston pump is disclosed which comprises a yoke includinga yoke bearing located at an opening of the yoke, a pump housingconnected to the yoke and including a first pump housing bearing locatedin the pump housing. An armature shaft extends between the yoke bearingand the first pump housing bearing and includes an eccentric shaft tipportion, and a second pump housing bearing, smaller in diameter than thefirst pump housing bearing, located on the eccentric shaft tip portionof the armature shaft. An inner cylinder portion of the pump housingcomprises the sequential formation of a first pump housing bearingsupport portion by which the first pump housing bearing is supported, asecond pump housing bearing moveable support portion which is smaller indiameter than the first pump housing bearing support portion and bywhich the second pump housing bearing is moveably supported, a temporarysupporting portion which is smaller in diameter than the second pumphousing bearing moveable support portion and configured to support thesecond pump housing bearing in a temporarily supported state and aninserting hole portion for inserting a jig from a side of the pumphousing that is opposite a side to which the yoke is connected and forpressing the jig against an inner ring of the second pump housingbearing to press fit the inner ring to the eccentric shaft tip portionof the armature shaft.

Such an arrangement allows a small through hole to be placed in thepiston housing for passing through a jig for pressing the inner ring ofthe second pump housing bearing, rather than a through holecorresponding with the outer diameter of the second pump housing bearingfor inserting the second pump housing bearing to one side thereof fromthe other side. While the second pump housing bearing cannot beassembled to the pump housing from the side opposite to the side towhich the yoke is assembled, this arrangement is advantageous in thatthe freedom in layout of the piston pump components provided within thepump housing is improved.

In accordance with a second aspect of the invention, the method ofassembly involves the steps of bearing one end of the armature shaft ofthe electric motor by a yoke with a yoke bearing, bearing the other endof the armature shaft by a pump housing with a first pump housingbearing, press fitting the one end of the armature shaft to an innerring of the yoke bearing, press fitting the other end of the armatureshaft to an inner ring of the first pump housing bearing, press fittingan outer ring of the first pump housing bearing to the pump housing, andassembling an outer ring of the yoke bearing to the yoke.

Such an arrangement does away with axial and radial direction wobblingof the bearings bearing the armature shaft even in the event that loadfrom the piston pump acts upon the armature shaft in the radialdirection, thus reducing noise and contributing to improved pumpperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional drawing of an electric motor in accordancewith a first embodiment of the invention;

FIG. 2 is a disassembled drawing of an electric motor in accordance witha first embodiment of the invention;

FIG. 3 is a drawing illustrating the assembly steps according to thefirst embodiment;

FIG. 4 is a drawing illustrating the assembly steps according to thefirst embodiment;

FIG. 5 is a drawing illustrating the assembly steps according to thefirst embodiment;

FIG. 6 is a drawing illustrating the assembly steps according to asecond embodiment of the invention;

FIG. 7 is a drawing illustrating the assembly steps according to thesecond embodiment; and

FIG. 8 is a drawing illustrating the assembly steps according to thesecond embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Next, the preferred embodiments of the invention will be described withreference to the drawings.

FIG. 1 shows a cross-sectional view of the electric motor for ananti-locking brake device. The electric motor 1 includes an armatureshaft 4 rotatably supported on one end by a yoke 2 and on the other endby pump housing 3. An armature core 5 and commutator 6 are assembledintegrally to the armature shaft 4. A brush 7 slidably contacts thecommutator 6, and a permanent magnet 8 is retained to the innercircumference surface portion of the yoke 2.

The yoke 2 is formed as a cylinder enclosed on the bottom. A bottomcylinder portion 2 b is formed to the bottom surface portion 2 athereof, and one end of the armature shaft 4 is rotatably borne by theinner circumference portion of the bottom cylinder portion 2 b with ayoke bearing 9. Further, a jig inserting hole 2 c, which is greater indiameter than the inner diameter of the yoke bearing 9, is provided atthe bottom portion of the bottom cylinder portion 2 b. Assembly of theyoke bearing 9 and the armature shaft 4 to this bottom cylinder portion2 b will be described later.

Pump housing 3 is integrally assembled to the opening side of the yoke2, with an inner cylinder portion 3 a formed to the pump housing 3 in ahollow traversing manner to the member coaxial with the shaft center αof the armature shaft 4. The other end of the armature shaft 4 protrudesinto the inner cylinder portion 3 a. The other side of the armatureshaft 4 is also rotatably borne by the pump housing 3 with a first pumphousing bearing 11. Assembly of the first pump housing bearing 11 andthe armature shaft 4 to the inner cylinder portion 3 a will be describedlater.

The pump housing 3 is mounted to various members comprising the pistonpump for an anti-locking brake device, such as a connecting rod, piston,cylinder and the like (all unshown).

An output end of the armature shaft 4 protrudes into the pump housinginner cylinder portion 3 a. The output end of the armature shaft 4protrudes farther into the pump housing 3 than the first pump housingbearing 11 and includes an eccentric output shaft portion 4 a, formedwith a center shaft β. The output shaft portion 4 a is smaller indiameter and is eccentric as compared to the center shaft α of thearmature shaft 4. Assembled to the eccentric output shaft portion 4 a isthe base end portion of the connecting rod, this being assembled theretowith a second pump housing bearing 12. Further, a piston is connected tothe tip portion of the connecting rod. Thus, the structure is arrangedsuch that the rotation of the armature shaft 4 causes the piston to movereciprocally within the cylinder in a radial direction with respect tothe armature shaft 4. Thus, the pump is driven and sends pressurizedbrake oil.

FIGS. 3 through 5 show the assembly steps of the electric motor 1. Thepump housing inner cylinder 3 a comprises a first pump housing bearingsupporting portion 3 b which fitably supports the first pump housingbearing 11 by press fitting next to the yoke 2. A second pump housingbearing moveable fitting portion 3 f is movably fit to the second pumphousing bearing 12 and is formed adjacent to the side of the first pumphousing bearing supporting portion 3 b which is deeper in the cylinder.An inserting hole 3 g is formed adjacent to the side of the second pumphousing bearing moveable fitting portion 3 f so that a jig can beinserted from the side opposite to the side to which the yoke 2 isattached. The outer ring 11 b of the first pump housing bearing 11 isthen press fit to the first pump housing bearing supporting portion 3 b,and subsequently the base unit 13 to which the brush 7 has beenassembled is assembled to the yoke assembly side surface of the pumphousing 3. Following this, the other side of the armature shaft 4 of thearmature assembly 14 comprised of the armature shaft 4, armature core 5,commutator 6, and the like integrally assembled, is press fit using thejigs A, B, and C to the inner ring 11 a of the first pump housingbearing 11 which has been assembled to the first pump housing bearingsupporting portion 3 b. The jigs are inserted from the through hole 3 gside (see FIG. 3). Jig A is a jig which is inserted from the side of thepump housing inner cylinder 3 a opposite to the side to which the yokeis attached, for supporting the inner ring 11 a of the first pumphousing bearing 11. Jig B is a jig for applying pressure to the one sideof the armature shaft 4, and jig C is a jig for guiding the other sideof the armature shaft 4 to the inner ring 11 a of the first pump housingbearing.

The outer ring 9 b of the yoke bearing 9 is attached to the innercircumference surface of the yoke bottom cylinder portion 2 b of theyoke unit 15 with a transition fit (light press fit) or clearance fit.The permanent magnet 8 is fixed beforehand to the inner circumferencesurface of the yoke 2. The axial direction movement of the yoke bearingouter ring 9 b is restricted by applying caulking 2 d to the openingedge portion of the bottom cylinder portion 2 b. However, no caulking isnecessary if the outer ring 9 b is attached with a press fit to restrictmovement.

Next, the inner ring 9 a of the yoke bearing 9 of the yoke unit 15 towhich the yoke bearing outer ring 9 b has been fit is then press fit tothe one end of the armature shaft 4 using jigs D and E (see FIG. 4). Thearmature shaft 4 is part of the armature assembly 14 assembled to thepump housing 3. Jig D is a jig for supporting the other end of thearmature shaft 4 and the pump housing 3. Jig E is a jig for beinginserted in the jig inserting hole 2 c of the yoke 2 and applyingpressure to the yoke bearing inner ring 9 a. The press fitting pressurefor press fitting the yoke bearing inner ring 9 a to the one side of thearmature shaft 4 using jig E is set to be equal to or less than themaximum axial load of the yoke bearing 9 and also equal to or greaterthan the press fitting load of the first pump housing bearing inner ring11 a. This pressure is continually applied until the opening edgesurface of the yoke 2 comes into contact at a predetermined pressurewith the bottom surface of the groove of the fitting groove 3 c formedon the yoke assembly side surface portion of the pump housing 3. Thepress fitting pressure at this time is set to be equal to or less thanthe maximum axial load of the yoke bearing 9 and also equal to orgreater than the press fitting load of the yoke bearing inner ring 9 a.

The fitting groove 3 c formed on the pump housing 3 is arranged suchthat the opening side edge portion of the yoke 2 movably fits into thefitting groove 3 c so as to form a spigot-joint fitting arrangement.Thus, even in the event that there is misalignment between the yokebearing 9 which is attached to the yoke 2 and the first pump housingbearing 11 which is press fit to the pump housing 3, the structure canhandle the misalignment due to the spigot-joint fitting arrangement.

Subsequently, the eccentric output shaft portion 4 a with the yoke unit15 assembled thereto is in the position of the second pump housingbearing movable fitting portion 3 f. The second pump housing bearing 12is inserted from the side of the inserting hole 3 g and press fit to theeccentric output shaft portion 4 a using the jigs G, J, and K, which arealso inserted from the side of the inserting hole 3 g (see FIG. 5). JigG is a jig for applying pressure to the one side of the armature shaft4, jig J is a jig for supporting the second pump housing bearing 12, andJig K is a jig for guiding insertion of the inner ring 12 a of thesecond pump housing bearing 12 to the eccentric output shaft portion 4a.

Following pressure fitting of the second pump housing bearing 12,through bolts 16 are inserted from the bottom surface portion 2 a sideof the yoke 2 and are screwed into the screw hole 3 d formed in the pumphousing 3 and tightened fast. Thus, the yoke 2 is integrally fixed tothe pump housing 3.

Also, in the Figures, reference numeral 17 denotes a couplerelectrically connected to the external power source side so as to supplyelectric power to the brush 7. Reference numeral 18 denotes awaterproofing cover which covers the entirety of the yoke 2 so as toprovide waterproofing to the electric motor 1. Reference numeral 19denotes a sealing member which is screwed to the inserting hole 3 g ofthe pump housing inner cylinder portion 3 a so as to cover up the hole.

Regarding the arrangement as described above, one end of the armatureshaft 4 of the electric motor 1 is rotatably borne by the yoke 2 sidewith a yoke bearing 9, and the other side thereof is rotatably borne bythe pump housing 3 with a first pump housing bearing 11. The inner ring9 a of the yoke bearing 9 is fit to the one side of the armature shaft4, and the outer ring 9 b thereof is attached to the yoke bottomcylinder portion 2 b. Also, the inner ring 11 a of the first pumphousing bearing 11 is press fit to the other side of the armature shaft4, and the outer ring 11 b thereof is press fit to the pump housingfirst pump housing bearing supporting portion 3 b. Any handling of themisalignment between the bearings 9 and 11 is performed by thespigot-joint fitting arrangement between the yoke 2 and the pump housing3.

As a result, the inner ring 9 a of the yoke bearing 9 and the inner andouter rings 11 a and 11 b of the first pump housing bearing 11 aremounted with a press fit so that even if a heavy load acts on thearmature shaft 4 in the radial direction due to the reciprocal movementof the piston which is driven by the motor, the bearings 9 and 11 do notwobble in axial and radial directions, as happens in conventionalarrangements. Thus, noise is reduced and pump performance is improved.In conventional arrangements, bearings are often assembled with freedomin the axial direction requiring retaining parts for restricting theaxial movement of bearings. In addition, resin material provided torestrict movement of the bearings in the axial and radial directionsrequires additional processes for inserting the resinous material, whichoften deteriorates. The disclosed electric motor needs neither retainingparts, nor a resin material for restricting axial movement of thebearings, and thus benefits from a reduction in the number of parts andreduction in the number of processes to manufacture the electric motor.

The disclosed invention is by no means limited to the above-describedfirst embodiment, wherein the yoke bearing outer ring 9 b is set to beattached to the yoke bottom cylinder portion 2 b with a transition fit,namely a light press fit, a clearance fit, or a through fitting. Thisarrangement may be press fit, which enables perfect restriction of themovement (rotation). However, when the outer ring 9 b is not press fit,the yoke bearing 9 is not a member for supporting the other side of thearmature shaft 4 upon which a load from the piston pump acts in a radialdirection, but rather is a member for supporting the one side of thearmature shaft 4 to the other side. Assembly and processing can besimplified as compared with press fitting.

A second embodiment of the invention is illustrated in FIGS. 6 through8. It should be noted that in the following description of the secondembodiment, the members which correspond to or are identical to those ofthe first embodiment are denoted by the same reference numerals.

In the second embodiment, the side opposite to the assembly side of theyoke of the pump housing inner cylinder portion 3 a has a small diameterso as to increase freedom of layout of the piston pump componentsprovided within the pump housing 3. According to this structure, thesecond pump housing bearing 12 cannot be assembled from the sideopposite to the side of yoke assembly. In other words, in the interiorcylinder portion 3 a of the pump housing 3, the following members aresequentially provided from the side of the yoke 2 toward the other sideso as to be in adjacent contact in the following order: the first pumphousing bearing supporting portion 3 b which has the greatest diameter;the second pump housing bearing moveable fitting portion 3 f with thenext greatest diameter to which the second pump housing bearing 12 ismovably fit; the temporary supporting portion 3 e with a yet smallerdiameter which supports both the second pump housing bearing 12 and thespacer 20, and the inserting hole 3 g through which the jig T forapplying pressure to the inner ring of the second pump housing bearing12 is inserted.

The second pump housing bearing 12 and the spacer 20 are inserted fromthe first pump housing bearing supporting portion 3 b side of theinternal cylinder portion 3 a and assembled to the temporary supportingportion 3 e in a temporarily supported manner. The width (thickness) ofthe spacer 20 is made to be equal to the axial distance between thefirst pump housing and second pump housing bearings 11 and 12 followingassembly of the electric motor 1. Also, the temporary supporting portion3 e is eccentric so as to correspond to the eccentricity of theeccentric output shaft portion 4 a. Jig U guides the second pump housingbearing 12 and the spacer 20 to the eccentric output shaft portion 4 a.

Next, the first pump housing bearing outer ring 11 b is press fit, usingjigs Q and R, to the first pump housing bearing supporting portion 3 bof the pump housing inner cylinder portion 3 a to which has beenassembled the second pump housing bearing 12 and the spacer 20 (see FIG.6). Subsequently, a base unit 13 is assembled thereto. Jig Q is a jigfor supporting the pump housing 3, and jig R is a jig for applyingpressure to the first pump housing bearing outer ring 11 b.

Further, using the jigs Q. S, T and U, the other end of the armatureshaft 4 of the armature assembly 14 is press fit to the inner ring 11 aof the first pump housing bearing 11 which has been press fit to thepump housing 3, and at the same time, the second pump housing bearinginner ring 12 a is press fit to the eccentric output shaft portion 4 a.Jig Q is a jig for supporting the pump housing 3 as described above, jigS is a jig for being inserted from the inserting hole 3 g and applyingpressure to the one end of the armature shaft 4, jig T is a jig forsimilarly being inserted from the inserting hole 3 g and applyingpressure to and also supporting the second pump housing bearing innerring 12 a, and jig U is a jig for similarly being inserted from theinserting hole 3 g and guiding the spacer 20 and the second pump housingbearing inner ring 12 a to the eccentric output shaft portion 4 a.First, jig S is used to apply pressure to one end of the armature shaft4 and insert the other end of the armature shaft 4 into the pump housinginner cylinder portion 3 a. At the point immediately before the armatureshaft 4 is press fit to the first pump housing bearing inner ring 11 a,jig T is used to press fit the spacer 20 and the second pump housingbearing inner ring 12 a to the eccentric output shaft portion 4 a untilthe spacer 20 abuts the first pump housing bearing inner ring 11 a.Further, when the first pump housing bearing inner ring 11 a issupported by jig T with the spacer 20 and the second pump housingbearing 12 being introduced therebetween, pressure is applied to the oneend of the armature shaft 4, thus performing press fitting of the otherend of the armature shaft 4 to the first pump housing bearing inner ring11 a using jig S (see FIG. 7).

Next, the yoke bearing outer ring 9 b is fit to the yoke bottom cylinderportion 2 b of the yoke unit 15 and is placed over the armature assembly14 which has been assembled to the pump housing 3, and the yoke bearinginner ring 9 a is press fit to the one end of the armature shaft 4 (seeFIG. 8), using the jigs Q, T, V, W, and X. Jig Q is a jig for supportingthe pump housing 3, jig T is a jig for supporting the second pumphousing bearing inner ring 12 a, jig V is a jig for applying pressure tothe yoke bearing inner ring 9 a, jig W is a jig for supporting the oneend of the armature shaft 4, and jig X is a jig for supporting the otherend of the armature shaft 4. Assembly according to the above stepsallows for the inner ring 9 a of the yoke bearing 9 and the inner andouter rings 11 a, 11 b, 12 a, and 12 b of the first pump housing and thesecond pump housing bearings 11 and 12 to be mounted with a press fitwithout obstruction, even if the construction is such that the sideopposite to the side of yoke attachment of the pump housing innercylinder portion 3 a is of such a small diameter that the second pumphousing bearing 12 cannot be assembled from the side opposite the yokeattachment. Further, according to this arrangement, due to theconstruction being such that the side opposite to the side of yokeattachment of the pump housing inner cylinder portion 3 a is made to beof a small diameter, the second pump housing bearing 12 cannot beassembled from the side of the inserting hole 3 g as with the firstembodiment. Accordingly, it is necessary to cause the temporarysupporting portion 3 e to temporarily support the spacer 20 and thesecond pump housing bearing inner ring 12 a. The diameter of theinserting hole 3 g needs only to be of a diameter large enough fortemporary insertion of jig T for applying pressure to the inner ring 12b of the second pump housing bearing 12. This arrangement isadvantageous in that the distribution space of the piston pumpcomponents provided within the pump housing 3 is expanded, resulting inimproved freedom in layout.

The invention has been described with reference to the above describedpreferred embodiments, which are meant to be illustrative, not limiting.Various modifications can be made without departing from the spirit andscope of the invention as defined in the appended claims.

What is claimed is:
 1. A method for assembling an electric motor fordriving a piston, wherein the electric motor for driving a pistonincludes: a yoke including a yoke bearing located at one end of theyoke; a pump housing connected to other end of the yoke and including afirst pump housing bearing located in the pump housing; an armatureshaft extending between the yoke bearing and the first pump housingbearing and including an eccentric shaft tip portion protruding from thefirst pump housing bearing and receiving a load for driving the pistonin a radial direction; and a second pump housing bearing, smaller indiameter than the first pump housing bearing, located on the eccentricshaft tip portion of the armature shaft, the method comprising: pressfitting an outer ring of the first pump housing bearing to the pumphousing; assembling an outer ring of the yoke bearing to the yoke; pressfitting one end of the armature shaft to an inner ring of the yokebearing; press fitting the other end of the armature shaft to an innerring of the first pump housing bearing; thereby bearing the one end ofthe armature shaft of the electric motor by a yoke with a yoke bearing;and bearing the other end of the armature shaft by a pump housing with afirst pump housing bearing.
 2. The method of claim 1, wherein the outerring of the yoke bearing is assembled to the yoke by at least one of atransition fit, light press fit, through fit and a clearance fit.
 3. Themethod of claim 1, further comprising the step of adding a restraint torestrict movement of the outer ring of the yoke bearing in an axialdirection.
 4. The method of claim 3, wherein the step of adding arestraint includes the step of applying caulking to an opening edgeportion of a bottom cylinder portion of the yoke to retain the outerring of the yoke bearing in the yoke.
 5. The method of claim 1, whereinthe steps of press fitting the one end of the armature shaft to an innerring of the yoke bearing and press fitting the other end of the armatureshaft to an inner ring of the first pump housing bearing furtherincludes the steps of applying a first predetermined pressure to theinner ring of the yoke bearing using a first jig and applying a secondpredetermined pressure to the inner ring of the first pump housingbearing using a second jig.
 6. The method of claim 1, further comprisingthe step of forming a spigot-joint fitting arrangement between the pumphousing and yoke.
 7. The method of claim 1, further comprising pressfitting the second pump housing bearing onto the eccentric shaft tipportion protruding from the first pump housing bearing.
 8. The method ofclaim 7, wherein the step of press fitting the second pump housingbearing onto the eccentric shaft tip portion includes: temporarilysupporting the second pump housing bearing within a temporary supportingportion of the pump housing; inserting a jig from an inserting holeportion formed on a side of the pump housing that is opposite a side towhich the yoke is connected; pressing the jig against an inner ring ofthe second pump housing bearing which is temporarily supported; pressingthe inner ring of the second pump housing bearing onto the eccentricshaft tip portion of the armature shaft supported by the pump housingwith the first pump housing bearing; and fitting moveably the secondpump housing bearing into a second pump housing bearing moveable supportportion of the pump housing.